Pervaporation membranes with poly(γ-benzyl-L-glutamate) selective layers for separation of toluene-n-heptane mixtures

New composite membrane with a poly(gamma-benzyl-L-glutamate) (PBG) separation layer on a micro-porous poly(amide-imide) support was prepared and tested as a pervaporation membrane for selective separation of toluene/n-heptane mixtures. Composite membrane was formed by coating a solution of PBG in chloroform on the top surface of micro-porous PAI-SO2 support. PBG layer fulfils indispensable requirement for the preferential adsorption of the most penetrating component (toluene) of a separated mixture. The structure of the membrane was studied in detail. X-ray diffraction, electron microscopy and IR spectroscopy measurements were performed. Crystalline regions formed by backbones of macromolecules are low permeable barriers to penetrants, but also limiters for swelling of high permeable polymer phase. The knowledge of the material structure in dependence of conditions of its preparation enabled to adapt the process of the membrane formation to reach the efficiency of separating aromatic/aliphatic compounds. The separation ability was tested by pervaporation measurements for different toluene concentrations in binary mixtures toluene/n-heptane. Diffusion coefficients, fluxes and separation factors were evaluated. It was shown that conformation of alpha-helix PBG molecules in the coating layer of the composite membrane does not change in the pervaporation. The membrane retains its integrity and can be used in subsequent cycles of a process. The obtained results during this study could be used for the design of highly efficient PBG/PAI-SO2 composite membranes for separation of mixtures aromatic and aliphatic hydrocarbons by pervaporation. (C) 2014 Elsevier B.V. All rights reserved.